JPH0337394B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an inverter device for controlling and driving an AC motor, and more particularly to an inverter device equipped with a power regeneration circuit.

[Conventional technology]

A conventional inverter device for variable speed operation of a conventional AC motor (induction motor or synchronous motor) was constructed as shown in FIG. In Fig. 4, 1, 2, 3 are three-phase AC power lines, 4 is a forward conversion circuit, 5 is an inverse conversion circuit, 6 is an AC motor,
7 and 8 are a pair of DC lines, 9 is a voltage smoothing capacitor, 10 is an energy release resistor, 11 is a transistor, and 12 is a voltage detection circuit. In addition,
The inverse conversion circuit 5 includes a three-phase bridge-connected transistor Q and a power regeneration diode D.

In this circuit, when the motor 6 operates as a generator when it is stopped or decelerated,
The voltage generated in the winding of the motor 6 turns on the diode D, and the regenerated energy is absorbed by the capacitor 9. When the regenerated energy is large and the voltage between the DC lines 7 and 8 becomes higher than a predetermined value, the output of the voltage detection circuit 12 causes the transistor 11 to
is controlled to be on, energy is consumed by the resistor 10, and regenerative braking is achieved.

[Problem that the invention seeks to solve]

When the circuit of FIG. 4 frequently enters the regenerative control state, current frequently flows through the resistor 10, causing an abnormal rise in temperature. Therefore, the power capacity of the resistor 10 had to be increased. In addition, in order to prevent the transistor 11 from turning on in response to ripples in the voltage V _D between the pair of DC lines 7 and 8 during normal operation, a reference voltage (reference voltage ) The _VDS level had to be set high as shown by the dotted line in Figure 2. Therefore, there were problems that regeneration did not start quickly and that the withstand voltage of the capacitor 9 had to be increased. As mentioned above, due to the large capacity of the resistor 10 and the high withstand voltage of the capacitor 9, when these elements become large, the inverter device as a whole becomes large even if the forward/inverse conversion circuit is made small. Further, since energy is consumed by the resistor 10, it is not possible to improve overall efficiency. SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inverter device that can quickly and appropriately perform regeneration control with little power loss.

[Means for solving problems]

The inverter device of the present invention for achieving the above objects includes a forward conversion circuit consisting of a forward conversion rectifier connected to an AC power source, and a power regeneration circuit connected antiparallel to the forward conversion rectifier. an inverse conversion circuit comprising a switch element, an inverse conversion switch element connected between a pair of DC lines of the forward conversion circuit and an AC motor, and a rectifier element connected in antiparallel to the inverse conversion switch element; , a capacitor connected between the pair of DC lines, a DC voltage detection circuit that detects the voltage between the pair of DC lines, and a direction of current flowing in the DC line between the capacitor and the inverse conversion circuit. a current direction detection circuit that detects that the current direction has become reversed; a reference voltage generation circuit that generates a voltage indicating a level to turn on the regeneration switch element; and a DC detection voltage obtained from the DC voltage detection circuit. a voltage comparison circuit that compares the reference voltage obtained from the reference voltage generation circuit and determines whether or not there is a voltage relationship that allows power regeneration through the power regeneration switch element; A period during which a signal indicating that the direction of the obtained current is opposite and a signal indicating that the power regeneration switch element obtained from the voltage comparison circuit can be operated for power regeneration are generated at the same time. and a regeneration control circuit that controls the power regeneration switch element to be in an on state.

[Effect]

In the above inverter device, when the electric motor is rotating normally, the DC output voltage of the forward conversion circuit is converted into AC by the inverse conversion circuit. When the motor enters the regenerative control state, regenerative energy is returned to the capacitor through the regenerative rectifier. If the direction detection circuit detects that regeneration is in progress and at the same time detects that the DC voltage is higher than the power supply voltage, the regeneration switch element is turned on only within this period, and the regeneration energy is is returned to the AC power source. Since the device of the present invention is provided with a current direction detection circuit, regeneration control is not performed solely in response to the magnitude of the DC voltage. That is, it is possible to determine whether the voltage of the DC line is high due to ripples during normal operation or whether the voltage is high based on regeneration. Therefore, regeneration control is performed quickly and appropriately.

〔Example〕

Next, FIG. 1 showing an inverter device according to an embodiment of the present invention will be described. However, in FIG. 1, the parts indicated by reference numerals 1 to 9 are substantially the same as those shown by the same reference numerals in FIG. 3, so their explanation will be omitted.

In addition to the first to sixth diodes D ₁ to D ₆ as bridge-connected rectifying elements, the forward conversion circuit 4 includes:
It includes first to sixth transistors _Q1 to _Q6 as power regeneration switch elements. The first to sixth transistors _Q1 to _Q6 are connected to the first to sixth diodes _D1 to _D6.
are connected in antiparallel to each other, and reverse conversion control is performed during regeneration.

In addition to the 7th to 12th transistors Q ₇ to _{Q 12} as inverse conversion switch elements connected in a three-phase bridge, the inverse conversion circuit 5 also includes a power regeneration rectifier connected in antiparallel to these transistors. 7th to 12th diodes _D7 to _D12 .

Reference numeral 13 denotes a DC voltage detection circuit, which is connected to a pair of DC lines 7 and 8 and generates a DC voltage _VD .

Reference numeral 14 denotes a current direction detection resistor, which is connected in series to the DC line 8 between the capacitor 9 and the inverse conversion circuit 5. Reference numeral 15 denotes a current direction detection circuit, which detects the direction of current according to the direction of the voltage across the resistor 14, and generates a high level output when the direction is in the opposite direction.

15a is a reference voltage generation circuit, which consists of a rectifier circuit connected to AC power lines 1, 2, and 3;
Generates a reference voltage V _DS corresponding to the AC power supply voltage.

A comparison circuit 16 compares the DC voltage V _D detected by the voltage detection circuit ₁₃ with the reference voltage V _DS obtained from the reference voltage generation circuit 15 and shown by the solid line in FIG. This is a circuit that generates a high level output when the detected DC voltage V _D becomes high.

17 is a regeneration control circuit, which includes three comparison circuits 18, 19, and 20 that function as signal sources, and three switches 21, 22, and 23 that function as AND gates.
, three NOT circuits 24, 25, 26 for obtaining an inversion control signal, and three NOT circuits 24, 25, 26 for determining the regeneration period.
The six output lines are connected to the bases of the first to sixth transistors _Q1 to _Q6 .

28, 29, and 30 are phase current detectors for each phase, which are provided to detect instantaneous values of regenerative current.

Reference numeral 31 denotes a reference phase current signal generation circuit, which detects line voltages of current lines 1, 2, and 3 using, for example, a transformer, and generates a phase voltage having a phase delayed by 30 degrees with respect to the line voltage, for example, using a transformer. Obtained by secondary winding,
This circuit generates a reference phase current signal indicating a phase current that matches this phase voltage.

The comparison amplifier circuits 18, 19, 20 compare the detected phase current signals obtained from the phase current detectors 28, 29, 30 of each phase with the reference current signals obtained from the reference phase current signal generation circuit 31, and When the current signal _ID is smaller than the reference phase current signal _IS , a high level output is generated, and when the opposite is true, a low level output is generated.

Next, the operation of the circuit shown in FIG. 1 will be explained. Now, assuming that the motor 6 is rotating normally and is not in a regenerative braking state, the three-phase alternating current is converted to direct current by the forward conversion diodes _D1 to _D6 , and this direct current is passed through the transistor _Q7.
It is converted to three-phase alternating current at ~Q ₁₂ . During this period, regenerative transistors Q ₁ to Q ₆ and regenerative diodes
_D7 to _D12 are kept off.

On the other hand, in the regenerative state, the detected voltage between the pair of DC lines 7 and 8 obtained from the voltage detection circuit 13
V _D becomes higher than the reference voltage V _DS , and the comparator circuit 16
The output of the direction detection circuit 15 becomes high level, and the direction detection circuit 15
produces a high level output indicating reverse current. And these two high level outputs
In order to input to the AND gate 27, the output of the AND gate 27 becomes high level, and the first, second, and third switches 21, 22, and 23 are turned on, and the transistors _Q1 to _Q6 are controlled. It becomes possible to supply signals. Since the regeneration state is determined by considering the direction of the current instead of detecting it only by voltage, it is possible to distinguish between ripple and voltage rise during regeneration, and the reference voltage V _DS for regeneration detection can be set as 2
As shown by the solid line in the figure, it can be set as low as the ripple.

The comparison circuits 18, 19, and 20 of each phase compare the regenerative current signal I _D and the reference current signal I _S as shown in Fig. 3, and when the detected current signal I _D is lower than the reference current signal I _S , the level is high. Generates an output and generates a low level output when high.

If the output of the comparison circuit 18 is now at a high level and the switch 21 is on, the first transistor _Q1 is turned on and a regenerative current flows.
At this time, the NOT circuit 2 is connected to the second transistor Q ₂ .
A low level signal is supplied via 4 to keep it off. When the transistor Q ₁ is turned on and the detected current signal _ID becomes larger than the reference current signal _IS , the output of the comparison circuit 18 becomes low level and the transistor Q ₁ is turned off. Since the regenerative current is instantaneously controlled in this way, it is possible to perform regeneration in which the phases of the phase voltage and phase current match, that is, regeneration with a power factor of 1.

The same control as the comparison circuit 18 is performed in the comparison circuits 19 and 20 of the other phases as well.

When the electric motor 6 stops or rotates normally,
When reverse current is no longer detected, switch 2
Since transistors 1, 22, and 23 are controlled to be off, transistors _Q1 to _Q6 are also kept off.

Although the embodiments of the present invention have been described above, the present invention is not limited thereto and may be further modified. For example, transistors Q ₁ to _{Q 12}
Instead, a self-extinguishing thyristor, FET, etc. may be used. 3 switches 21, 22, 2
Instead of three switches, six switches may be provided in total for the transistors _Q1 to _Q6 . Comparison circuits 18, 19,
Instead of generating a controlled output from 20, a power source is provided that always generates a high-level or low-level voltage, and based on this, a control signal is formed to distribute the transistors Q ₁ to _{Q 6} to operate as an inverter. , the output of the AND gate 27 may be used to control whether or not this control signal is supplied.

〔Effect of the invention〕

As is clear from the above, according to the present invention, the power regeneration switch element parallel to the forward conversion rectifier is controlled based on voltage detection and current direction detection to return regenerated energy to the AC power source. It is possible to reduce consumption. Since the start of regeneration is not decided based on voltage alone, but the direction of current is taken into consideration, the voltage level at which regeneration is started can be lowered, and regeneration can be controlled quickly and accurately. Note that by lowering the voltage level at which regeneration starts, the withstand voltage of the capacitor between the pair of DC lines can be lowered. Furthermore, since a resistor for consuming regenerated energy is not required, the device can be made smaller.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an inverter device according to an embodiment of the present invention, FIGS. 2 and 3 are waveform diagrams of various parts of FIG. 1, and FIG. 4 is a block diagram of a conventional inverter device. 1, 2, 3... AC power line, 4... Forward conversion circuit, 5... Inverse conversion circuit, 6... AC motor,
7, 8...DC line, 9...Capacitor, 13
... DC voltage detection circuit, 14 ... Current direction detection resistor, 15a ... Reference voltage generation circuit, 16 ... Comparison circuit, 17 ... Regeneration control circuit.

Claims (1)

[Scope of Claims] 1. A forward conversion circuit comprising a forward conversion rectifier connected to an AC power source; a power regeneration switch element connected in antiparallel to the forward conversion rectifier; and a power regeneration switch element connected in antiparallel to the forward conversion rectifier; an inverse conversion circuit consisting of an inverse conversion switch element connected between a pair of DC lines and an AC motor; a rectifier element connected in antiparallel to the inverse conversion switch element; and a rectifier element connected between the pair of DC lines. A connected capacitor, a DC voltage detection circuit that detects the voltage between the pair of DC lines, and a DC voltage detection circuit that detects that the direction of the current flowing in the DC line is reversed between the capacitor and the inversion circuit. a current direction detection circuit for detection; a reference voltage generation circuit for generating a voltage indicating a level for turning on the regeneration switch element; and a DC detection voltage obtained from the DC voltage detection circuit and a DC detection voltage obtained from the reference voltage generation circuit. a voltage comparison circuit that compares the voltage with a reference voltage and determines whether or not there is a voltage relationship that allows power regeneration through the power regeneration switch element; and a voltage comparison circuit that compares the voltage with a reference voltage and determines whether or not the voltage relationship is such that power can be regenerated through the power regeneration switch element; The power regeneration switch element is activated within a period in which a signal indicating that the power regeneration switch element is capable of operating the power regeneration switch element obtained from the voltage comparison circuit and a signal indicating that the power regeneration switch element can be operated for power regeneration obtained from the voltage comparison circuit are generated simultaneously. An inverter device consisting of a regeneration control circuit that controls the on state.